1. Field of the Invention
The invention generally relates to shock absorbing overtravel stops for aircraft actuators, and more specifically, to the type of shock absorbing overtravel stop wherein a travelling nut is moveable along a screw shaft.
2. Background of the Invention
It is known that in the actuation of the control surfaces of aircraft, some type of overtravel stop is required to prevent damage which may result to the aircraft structure or the flight control surfaces when the normal operating range of the control surface is exceeded.
The use of an overtravel stop using a travelling nut on a screw shaft to limit the number of revolutions which a shaft may make in either direction is well known. Such stop mechanisms usually require some type of energy absorber to cushion the drive train from the high torque spikes which result when the stop is suddenly engaged by a nut. This is often accomplished through the use of a torsional shock absorber or a long torsion rod as exemplified in U.S. Pat. No. 4,064,981 issued Dec. 27, 1977 to House et al.
House discloses a limit stop apparatus wherein a driven shaft rotates a predetermined number of revolutions in either direction whereupon a travelling nut assembly contacts a shock absorbing stop, made up of energy absorbing rotating and stationary discs, at either end of the screw shaft to terminate shaft rotation by frictionally jamming threads between the nut assembly and the driven shaft. As the shaft is driven at a location remote from the nut when the latter is against either stop, the length of the shaft between the nut and the drive torsionally absorbs the shock. A problem with this prior construction is the increased weight which is a necessary consequence of the use of a shock absorbing stop at each end of the shaft.
Further, the use of a separate torsion rod is not advantageous since the combined length of the torsion rod and stop screw can become prohibitively long.
The present invention is directed toward overcoming one or more of the problems as set forth above.